Liquid oxygen explosive and methods for preparing same



Feb. 3, 1959 F. 1 SHEA, JR 2,872,305

LIQUID OXYGEN EXPLOSIVE AND METHODS FOR PREPARING SAME Filed Oct. l5i 1957 LIQUID OXYGEN EXPLOSIVE AND METHODS FOR PREPARING SAME Frederick L. Shea, Jr., Arlington Heights, Ill., assigner to Great Lakes Carbon Corporation, New York, N. Y., a corporation of Delaware Application October 15, 1957, Serial No. 690,302V

8 Claims. (Cl. 52-1) This invention relates toa process for preparing liquid oxygen explosives. More particularly, this invention relates to a process for preparing liquid oxygen explosives in which va specially prepared absorbent carbon is employed. p p

Mixtures of highly volatile oxidizing agents such as liquid oxygen, liquid air or liquid ozone with a combustible substance, such 'las nely divided carbon, have previously been proposed as explosives. This type of explosive is ordinarily employed by forming cartridges of the nely divided carbon, soaking the cartridges in liquid oxygen or other volatile oxidizing agents and then within a short time using the saturated cartridges in blasting operations. This kind of explosive is not only powerful but has -certain advantages over other types of explosives. Since the components of these explosives are mixed at the site where they are to be used and since these components are not alone likely to explode, all hazards resulting from the transportation of` an explosive mixture :are avoided. Also, if the prepared charge fails to detonate for yany reason the charge is rendered harmless by the subsequent evaporation of the volatile oxidizing agent. However, the employment of explosives of this type in the past has been dangerous due to the fact that the mixture of carbon and liquid oxygen, in most cases, is easily detonated by impact or friction. Accordingly, there is a great danger of premature `explosions caused by rocks or other objects falling on the explosive mixture while it is being lowered into drill holes or by other shocks Y accidentally transmitted to the `mixture such as by friction against the walls of the drill hole, etc.

Attempts have been made to desensitize liquid oxygen explosives by diluting the absorbent carbon with inert absorbents. -For the same reason attempts have been made to lire proof the absorbent carbon by coating or impregnating with various chemicals.V These attempts to desensitize or tire proof the carbon have not only been costly but also have not 'been entirely effective andusually results in loss of performance, particularly detonation velocity. i

It is, therefore, an object of this invention to provide a process for producing an explosive of theliquid oxygen type which without the addition of desensitizing orv lireprooling agents, is less sensitive to detonation by impact or friction than lany previously known liquid oxygen explosive.

lt is a further object of this invention to provide a process for producing a liquid oxygen explosive which, despite the fact that it is relatively safe to handle, is nevertheless effective, when properly detonated, with respect to its disruptive or shattering properties.

It is a further object of this invention to provide a process for producing a-liquid oxygen explosive in which a hard, granular carbon4 is prepared which is sufciently absorbent with respect to liquid oxygen or similar volatile oxidizing agents to function safely and eectively in said explosive.

The above objects,` as well as others which will be- 2,872,305 Patented Feb. 3, 1959` come apparent upon an understanding of the invention as herein described, `are accomplished by ash-calcining in a gaseous atmosphere containing a limited and controlled amount of oxygen, `a nely divided bituminous feed material normally solid at ordinary temperatures and capable of expanding on heating the particles to plasticity; followed by separating the resulting solid particle material from the gaseous, vaporized products at a temperature above that at which said products will condense and redeposit upon the calcined particles. In an optional operation, the partially devolatilized expanded y coked particles are heated to further reduce their Volatile content. Liquid oxygen or other equivalent volatile oxidizing agent is then caused to be absorbed by the resulting hard, granular absorbent carbon.

AThe term flash-calcination (first stage reaction) as used herein and in the appended claims may be defined as a method whereby finely divided particles of a suitable 'bituminous material are subjected to a very rapid upheat rate, estimated to be in excess of 2000" F. (particle surface temperature) per second, in a reactor maintained at a temperature of 1150 F. or higher, but suicient to ignite 'the particles. The rapid upbeat of the particles is conducted in the lpresence of air or other oxygen-containing gas (or oxidizing gas) the oxygen being present in an amount such that at least 10% of the evolved combustible volatile matter remains unburned. The amount of air or oxygen present is sumcient to make the process selfsustaining while permitting expansion of the individual bituminous particles at a rapid rate but is insucient to permit more than a minimum burning of the individual expanded first-stage product particles. In general, it has been observed that higher temperatures within the aforementioned range may be employed when larger particle size feed material is used.

In a broad embodiment of the invention, finely divided bituminous feed material which is normally solid at ordinary temperatures but which is capable of expanding on heating to plasticity, is processed in two stages.- In the first stage, the feed material is ash-calcined within the aforementioned temperature range and in a gaseous atmosphere containing oxygen in an amount such that at least 10% of the evolved combustible volatile matter remains unburned.

In the second stage of the process the expanded particles produced in the rst stage are separated from gaseous and vaporous products at a temperature not less than that at which substantially all of the vaporous products of the first stage remain in the vaporous state. This temperature will vary with the type of feed material employed and is intended to be high enough to minimize condensation of the vapors on the -expanded particles. It is essential that the temperature in the second stage be such that the volatile content of the particles resulting from this stage of the process have a volatile content of 12% or less, as defined herein. This is normally achieved by heating the particles -suiiciently in the rst (flash-calcination) stage so that not more than about 12% by weight of volatile material remains on the particles themselves, the remaining volatile matter being present in the form of burned or unburned gases which are removed in the second stage; or alternatively operating the second stage at -a sumciently high temperature to not only strip olf the gaseous and/or vaporous materials from the product stream, but also maintaining the temperature within the second stage sufficiently high to remove additional volatile matter from the particles themselves in order to expanded particles separated in the second stage are giveny a further heat treatment to reduce their volatile content to .less .than 5%. The resulting hard, granular, essentlally non-activated absorbent carbon is then placed in a suitable cartridge or other container and saturated with liquid oxygen: or similarequivalent volatile oxidizing agent such as.liquirl air or liquid ozone.

Theloose bulk density of the hard, granular, absorbent carbon prepared in my process should have a value between '5 to 20 lbs/cu. ft.

We 4have found that the type of carbon desired can best be produced where the tiash-calcining temperature inthe first stage is maintained at no less than about 115()D F. vand no Amore than about 2000 F., the temperature varying with the feed size and type of bituminous material used. Employment of too low a temperature will result in an insufciently expanded product. Use of too high a temperature will result -in undue shrinkage or collapse of the particles and -a consequent excessively high bulk density of the product.

:Control of 'the temperature of heat treatment in the first :stage is `accomplished by regulating the oxygen intake. It has been found that the required amount of oxygen, in standard cu. fnl/lb. of bituminous material, is between about 2.0 and 4.0 when unheated air is used as` the source of oxygen. Lesser amounts of oxygen can be used Vifeither the feed or the air or oxygen intake are preheated or if the source of oxygen be relatively pureoxygen .or oxygen enriched air, etc. In any event, the oxygen should be present only in such an amount that at least '10% of the evolved combustible volatile matter remains unburned. This unburned volatile matter is separated from the expanded particles in the second stage separator from which it is conveyed to some disposal point such as combustion chamber 26 illustrated in the drawing. By thus limiting the burning of evolved combustible volatile matter in the first stage, reactor temperatures can be maintained -suiciently low (2000 F. or lower, `to avoid the aforementioned shrinkage or collapse of the bituminous particles.

I have found that when the expanded particles contained from the first and second stage process have a volatile `content of about 12% or less, as defined herein, such carbon will be an absolutely safe absorbent for liquid oxygen explosive. Further processing of the second stage product by calcinng in a third stage, as described herein, will further reduce the volatile content of the particles in the event that some users consider a low volatile content of the particles to be essential. The two-stage method of this invention results in substantially higher yields and product quality (i. e. lower Ibulk density) than can be achieved in, for example, a single stage process in which both expansion of the coal particles and a comparatively low volatile content would be sought in one stage. Also, lthe present method for producing absorbent carbon makes possible the controlled expansion of the bituminous particles in the first stage and control of the volatile content of the resulting calcined, expanded particles in the second stage.

While it is preferable that the source of heat used in each of the stages be the particle itself, it is -within the contemplation of this invention that a portion of the heat may be supplied by some outside source or auxiliary fuel. The most rapid upheat rates are, of course, obtained using the particle itself as the source of heat.

The raw material employed in producing this absorbent carbon may be any finely divided bituminous material normally solid at ordinary temperatures and capable of expanding on heating to plasticity. By the latter is meant the ability of the material to soften when heated through the plastic state and swell if the volatile matter of each particle is driven off at a sufficiently high rate. Examples of such materials include both low, medium and high volatile bituminous coals, raw co'al tar pitch coke, and coal tar pitch fortified with any of the various thermal blacks or carbon blacks. In any event the processing history of the raw material selected must not include `heating yat a temperature -or time .great enough `to Aresult in a permanently set carbonaceous structure. Any raw material subjected to such temperature conditions will not expand satisfactorily on heating to plasticity under the conditions disclosed herein.

The aforesaid raw materialemployed in preparing the absorbent carbon should not-have too high an ash content since mineral impurities in toogreat an amount may result in a carbon of unfavorable detonating characteristics. In general, it 'may be stated that no raw material should be used which will result in an absorbent carbon product having an ash content of'more than'about 15% by weight.

In preparing the bituminous material described above for the rst stage Hash-'calcination operation, the material must be suitably ground or milled to produce finely divided particles. This involves the use of a Raymond ring roller mill, `r`Babcock and Wilcox ball ring mill or other appropriate 'plverizing apparatus which will reduce thebituminous material 'to va particle size of about V--190 mesh (Tyler sieve) and preferably about 65 to 95% -200 mesh. It has been found that the latter size of 'feed is to be preferred in order to produce from the coal a final absorbent carbon product which will have a particle size 'falling within the range of 5 to 14() microns, very little of the product falling outside of this range. I also contemplate under certain circumstances the milling and classification (by either dry or wet methods) -of the `bituminous feed.

In preparing the absorbent carbon by theprocess described herein, I have found that yparticularly beneficial results are `to be obtained by maintaining the moisture content of the raw material at a value of yless than 5% by weight. 'Excess moisture in the bituminous material fed to the unit in which'the flash-calcination is conducted necessitates vaporization ofthe Water to la 'temperature above fl` F., or whatever reactor temperature used, which sharply reduces the rate of temperature rise of the bituminous particles. Often vthis must ybe done by burning additional fuel in the unit since excess moisture in the particles reduces the temperature of the operation to apoint Where the desired results are not obtained.

The absorbent carbon, whose process `of manufacture is described herein, should preferably lhave `a particle size of at least about 60% -200 mesh. More narrow particle size limitations maybe appropriate for certain blasting operations. For example, an explosive of higher brisance may be obtained when ythe absorbent carbon is of a smaller particle size. However, when such ksmaller particle-size is employed it may be necessary to adjust other physical characteristics of the particles to 'maintain a sufficiently low impact resistance for safety reasons.

A 'further requirement of the absorbent carbon produced by the process 'of my invention vis that it have a bulk density between 5 to 2'() lbs/cu. ft. Bulk density values are Vdetermined by permitting the product to fall freely into a graduated cylinder and measuring the loose-settled volume of a given weight of the product.

In a preferred embodiment of my invention, finely divided bituminous coal having a volatile content of between about l5% and about 20%, is ilash-calcined by entraining in an air stream and feeding it into the top of avertical reactor. Secondary air is supplied to the reactor to give a total oxygen content of between 2.2 and' about 3.5 standard cu. ft./lb. of coal and to produce a reactor temperature between about l350 and about l6S0 F. The residence time of the particles in the reactor will vary from a fraction of a second to not more than about 3 seconds. The expanded solid product of this rst stage is then separated from the gaseous products in a cyclone collector operated at a temperature not less than that at which substantially all of the vaporous products remain in the vaporous state. By maintaining the cyclone collector (second stage) at a temperature above Athe condensation point or dew point of the vaporous products expelled from the particles in the first stage, it is possible to strip off these products and produce a solid material having a volatile content of about 12% or less which is highly useful as an absorbent in carbon liquid oxygen explosives. The hard, granular, finely divided absorbent carbon produced is then packed in cloth cartridges and saturated with liquid oxygen to produce a safe but effective explosive composition.

In a further embodiment of my invention, and one which illustrates a 3-stage process is shown in the accompanying drawing in which the finely divided bituminous coal is fed into the top of pressurized feed hopper 12 having an agitator 13 (rotating shaft with radial spikes) and screw feeder 14. The coal feed from screw feeder 14 is entrained in an air stream and carried to the top of a rst stage reactor 15 into which it is injected preferably through a water cooled nozzle (not shown). Secondary air is added to reactor 15 at a position near the top of the reactor. Temperatures within this reactor are preferably between 1350 andl650 F. Blower 24 is employed to supply both the primary and secondary air streams through valves 27 and 28, respectively. The entrained product particles in reactor 15 are carried from the bottom of the reactor to cyclone 16 maintained at a temperature above the condensation point of the gaseous or vaporous products, where their separation is effected. The gaseous and vaporous products are removed from the top of cyclone 16 and passed into combustion chamber 26 where they are burned prior to escape through a stack. Air supplied by blower and controlled by valve 32 along with fuel gas is injected into the combustion burner to effect the burning of the gases. Blower 23 is employed prior to normal operation of the plant to supply fuel gas to auxiliary burners in 15 and 17 which bring the reactors up to oper- 3 ating temperatures.

The product of the second stage operation (cyclone 16) is removed through seal valve 30 and carried by an air stream, supplied by blower 24 through valve 31, to the top of reactor 17. Seal valve is necessary since reactor 15 and cyclone 16 are maintained under positive pressure whereas reactor 17 is maintained at a negative pressure (or a lower positive pressure) by blower 22 operating as an exhauster.

Secondary air is bled into reactor 17 through valve 33 in sucient quantity to maintain the reactor temperature at about 1300 to about 2300 F. The product of reactor 17 (third stage operation) is removed from the bottom of reactor 17 and carried to collector cyclone 18. Gaseous products from reactor 17 are carried from the top of cyclone 18 to scrubber 19 having water sprays 35, 36 and A37. Sludge from scrubber 19 is deposited in sludge pot 20 from ywhich it may be conveniently removed. The final absorbent carbon product passes from the bottom of cyclone 18 through valve 34 into a drum 21.'

In order to further illustrate the invention, but with no intention of being limited thereby, the following examples are set forth in which various bituminous materials were preliminarily ground to suitable particle size, with controlled moisture content, after whichthe comminuted material was processed in apparatus of the type or similar to that illustrated in the drawing. The absorbent carbon obtained was then saturated with oxygen and detonated under controlled conditions permitting measurement of `various explosive characteristics.

The following is an explanation of terms used in characterizing my explosive or the carbon used therein:

The volatile content of the coal and absorbent carbon, exclusive of water, was determined by ASTM Procedure No. D27l-48.

Detonation velocity was determined by measuring the time interval which elapsed between the breaking of two copper wires a known distance apart. This time .interval was measured with a Hewlett Packard type 522 ,75 actor 15 interval timer. Wires to be broken were No. 30 copper wires threaded through a 4 ft. long cartridge, there being a distance of 3 ft. between the two wires. A piece of primacord was inserted into the end of the cartridge so that it was about 4" from the start wire. This distance between the primacord aud wire is necessary in order to be sure that the wire is broken by the carbon and oxygen explosive rather than the primacord.

Low-velocity impact resistance indicates the resistance of the explosive composition to detonation by accidental impact and was determined in accordance with the procedures described in U. S. Bureau of Mines Bulletin 472, pages 20-27. In other words, this impact is required to accidentally detonate the composition. The explosive composition of my invention has a low-velocity impact resistance of 9000 ft. lbs. or more.

Burning in semi-confnemen indicates what may be expected if the explosive composition should be ignited after it has been loaded into the drill hole. A 1%" diameter pipe was capped at both ends and provided in one cap with varying degrees of pressure relief by drilling various holes. An explosive mixture contained' in the pipe was then ignited with a slow burning fuse and success or failureto detonate was noted. The smaller the orifice necessary for the burning to cause an explosion, the safer the explosive.

Oxygen absorption and retention: The ability of the absorbent carbon to absorb and retain liquid oxygen was determined by immersing a 2 ounce sample of the carbon contained in a lire-resistant cotton bag in liquid oxygen. After ten minutes the bag and contents were removed and immediately weighed to determine the initial oxygen: carbon ratio. A timer was then started and the bag was suspended from the balance to determine the time required for evaporation to decrease the oxygenucarbon ratio to 2.0. The value obtained serves as an index of the retention times that can be expected in commercial blasting operations wherein the cartridges and filling methods employed result in longer retention times. A long retention time is desirable since it allows more time to prepare the explosive charges priod to their detonation.

Example No. I

A sample of Affinity Mine bituminous coal having a volatile content of 16.75% and ash content of 4.3% was milled to -200 mesh. The first stage reactor 15 was preheated to a temperature of 1377" F. by burning gas supplied by gas pump 23 to auxiliary burners in the reactor. A stream of the coal was then fed into reactor 15 and processing carried out as described in the aforesaid preferred embodiment. The feed rate was 117 lbs./ hr. The maximum temperature in the rst stage (reactor 15) was l6l2 F. The minimum temperature in the second stage A(cyclone 16) was 805 F. A hard granular absorbent carbon was obtained in a yield of 58.0% based on the dry weight of feed to the first stage. This carbon had an ash content of 5.0%, a volatile content of 9.7% and a bulk density of 7.2 lbs./ cu. ft. Oxygen absorption tests showed the initial oxygenzcarbon ratio to be 4.5 and the Aoxygen'retention time 20 minutes. Tests on explosives prepared by immersing this carbon in liquid oxygen showed the low-velocity impact resistance to be more than 9200 ft. lbs. In semi-confinement tests, detonation failed to occur using an orifice of 1A" in diameter. The detonation velocity of the explosive was found to be 15,800 ft./second'.

Example N o. Il

A sample of Ainity Mine bituminous coal having a volatile content of 16.75% and ash content of 4.3% was milled to 75 200 mesh. The first stage reactor 15 was preheated to a temperature of 1377 F. by burning gas supplied by gas pump 23 to auxiliary burners in the reactor. A stream of the coal was then fed into reand processing carried out as describedin the asv-2,305

aforesaidgprferrd embodiment. The feed rate was 1.17 lbs.'/hr. The 'maximum 'temperature in the 'first stage (reactor 1'5) was 1612" F. The minimum ltemperature in the second stage (cyclone 16) was 805 F. The maximum yte'mp'era'tue in the third stage V(reactor 17) was 2394 F. hardfgranular absorbent carbon was obtained in a yield of 53.7% based on'the dry weight of feed to the iirst stage. This carbon had an ash content of 53%, avolatile'content of 1.18% 7and a bulk density of 13.3 lbs/cu. ft. Oxygen absorption s showed vthe initial xygencar'bon ratio to be 4.1 and the oxygen retention ti'riie Vllf' minutes. Tests 'on explosives prepared by'im'rnesing'thi's carbon -in'liqu'id oxygen showed `the low-velocity impact resistance to Vbe more than 9600 ft. lbs. LIn semi-confinement tests, detonalion failed to occur using'an orifice of Mi" in diameter. The detonation velocity of the explosive was found to be 15,800 ft./second.

Eltz'nple III A sample of Williams bituminous coal, seam No. 6. having a volatile content lof 37% by weight and ash content of 3% was milled to 49% 200 mesh and processed similarly to Example No. l. The first stage reactor temperature was 1460D F. The resulting product had a bulk density of 6.8 lbs/cu. ft., 'a volatile content or 12.0% and an ash content of 5.5%. Oxygen absorption tests indicated that the carbon had an initial oxygenzcaroon ratio of 4.1 yand an oxygen retention time of 18 minutes. Tests made on the explosive prepared by immersion of the carbon in liquid oxygen showed the explosive to have a low velocity impact resistance ot' more than 9500 ft. lbs. Burning in semi-confinement tests failed to detonate the explosive using an orifice of Mi diameter. was 14,010 ft./second.

Example IV A sample of Williams bituminous coal, seam No. 6, having a volatile content of 37% by weight and ash content of 3% was milled to 49% -200 mesh and processed similarly to Example No. l. The first stage reactor temperature was 146G F. However, instead of passing to the third stage vertical reactor, the particles from cyclone were calcined in a Bartlett-Snow kiln to reduce its volatile content. During the first 3.7 hours of calcinationthe temperature was gradually increased to 830 F. The V'calcination was then continued fortwo hours to a temperature of 830-1010o F. rl`he resulting product had a bulk density of 14.7 lbs/cu. ft., a volatile content of l3.6% and an* ash content of 7.6%. Oxygen absorption tests indicated Vthat the `carbon had an initial oxygenrcarbon ratio of v3.1 and an oxygen retention time of 11.6 minutes. Tests made on the explosive prepared lby immersion of the carbon in liquid oxygen showed the Vexplosive to liavea low velocity impact resistance of 'more than 9600 ft. lbs. Burning in semiconiinement tests failed to detona'te the explosive using an orifice 'of 1A" diameter. The detonation velocity of the explosive was 14,033 ft./ second.

Example N0. V

For purposes of comparison a carbon prepared from Wood bark and commonly used in Vliquid oxygen explosives after chemical treatment 'to make it lire-'proof was subjected to the aforesaid tests. Using a non-lire-proofed sample, it was found to have a bulk density of 12.0 lbs/cu. ft., and an ash content of 1.9%. Oxygen absorption tests indicated that its initial oxygenzcarbon ratio was 3.5 and oxygen retention time 12.0 minutes. A low-velocity impact test 'on a liquid oxygen explosive prepared with this -carbon produced explosions at 930 ft. lbs. In a semi-confinement test the explosive detonated when using an orifice ofi'f diameter but not with an orifice of 5/8" diameter. The 'd'etonation velocity was 18,000 :EL/second.

The detonation velocity of the explosive The explosives `prepared according to my invention and described `in -Einrnples fl and 4 were found Ato be highly effective `and `unusually f safe y"despite 4the Alack Aof anyfire-proofing treatment of "the a`bs0rbet carbon. Furthermore, my process rfor preparing Va liquidbxygen expl'osivefmakes possible the production of'an explosive of great flexibility of use. By the'adjustment of the bituminous feed `material -and reactor conditions, it is possible to prepare an explosive'with afmediurn or large safetyfactor coupled respectivelywith-ahigh or medium detonation velocity, `deps'endent on the particular yblasting requirements.

'For a lcomplete understanding of my invention, it-is pointed out that Vrthe reactor temperatures set-forth in the various embodiments of'my -invention'are the apparent atmospheric temperatures, rather than particle temperatures, and are measuredfby'means of thcrrnocouples inserted into theint'erior of the Yreactors through ceramic sealed Wells in the-reactor walls.

It is also to ybe Vunderstood that bituminous vniat'erials other than those described in the forego-ing examples may be used to produce the absorbent carbon employed in my invention, provided that these materials are capable of expanding on heating to plasticity. Also other conventional types of reactor units may be employed as long as they provide the temperature and atmospheric conditions specified in the broad embodiment set forth above. For example, alternative lto the vertical reactor 17 described in Figure 1, one may employ a thermal fluidizing unit, an externally fired rotary kiln, ora multiple-hearth furnace'of the type known as the Herreshof furnace in which the coal particles are passed vprogressively down through the unit while being subjected to -a stream of hot gases. It is also to be understood that the absorbent carbon employed in my invention may be classified (or milled and classified) by dry or wet methods in order to regulate the oxygen absorption characteristics.

One of the novel methods for preparing the absorbent carbon described herein for preparing a liquid oxygen explosive, is the subject of my co-pending application Ser. No. 502,122, filed April 18, 1955. In addition, this application is a continuation-in-part ofmy application Ser. No. 516,839 filed June 21, 1955, now abandoned.

Having thus described the nature of my invention, l claim:

1. The method of producing a liquid oxygen explosive which comprises .preparing a hard granular essentially non-activated absorbent carbon by a three-stage process from finely divided bituminous particles normally solid at ordinary temperatures and capable of expanding Aon heating to plasticity, said .process comprising in the first stage,flashcalcining the particles entrained in a gaseous atmosphere containing oxygen in an amount such that atleast 10% of the evolved combustible volatile matter remains unburned; in the second stage, separating the solid first-stage product from gaseous and vaporous products at a temperature not yless than that at which substantially all of said vaporous products remain in the vaporous state; and in the third stage, heating the solid second-stage lproduct to reduce its volatile content to less than 5% by weight; and thereafter causing liquid oxygen to be absorbed by the resulting absorbent carbon.

2. The method of producing a liquid oxygen explosive which comprises vpreparing a hard granular essentially non-activated absorbent carbon by -a three-stage process from finely divided bituminous coal, said process cornprising in the rst stage, iiash-calcining the coal particles entrained in a gaseous atmosphere containing oxygen and at a temperature between about l and about 2000o F. in an amount such that at least 10% of the evolved 'combustible volatile `rnatter remains unburned; in the second stage, separating the solid vfirst-stage products from gaseous `and vaporous products lat a tempera- 9 ture not less than that at which substantially all of said vaporous products remain in the vaporous state; and in the third stage, heating the solid second-stage product to reduce its volatile content to less than by weight; and thereafter causing liquid oxygen to be absorbed by the resulting absorbent carbon.

3. A process according to claim 2 wherein the bituminous coal has a volatile content between about to by weight.

4. A liquid oxygen-carbon explosive comprising essentially a hard, granular, essentially non-activated carbon saturated with liquid oxygen, said carbon having a loose bulk density between 10 and 20 lbs./cu. ft, a volatile content below 5% and an ash content below-8%, said carbon being prepared from finely divided bituminous coal by means of a 3 stage process comprising, in the rst stage, iash calcining the coal particles entrained in a gaseous atmosphere containing oxygen and at a temperature between about 1150 F. and about 2000" F. in an amount such that at least 10% of the evolved combustible volatile matter remains unburned; in the second stage, separating the solid first-stage products from gaseous and vaporous products at a temperature not less than that at which substantially all of said vaporous products remain in the vaporous state; and in the third stage, heating the solid second-stage product to reduce its volatile content below 5% by weight.

5. The method of producing a liquid oxygen explosive which comprises preparing a hard, granular, essentially non-activated absorbent carbon by a two-stage process from finely divided bituminous particles normally solid at ordinary temperatures and capable of expanding on heating to plasticity said process comprising in the rst stage ash-calcining the coal particles entrained in a gaseous atmosphere containing oxygen in an amount such that at least 10% of the evolved combustible volatile matter remains unburned; in the second stage, separating the solid first-stage products from gaseous and vaporous products at a temperature not less than that at which substantially all of the said vaporous `products remain in the vaporous state; and collecting the resulting solid product which is characterized by having a volatile content of less than about 12% by weight and a bulk density between about 5 to 20 lbs/cu. ft.; and thereafter causing liquid oxygen to be absorbed by the resulting absorbent carbon. y

6. The method of producing a liquid oxygen explosive which comprises preparing a hard, granular, esentially non-activated absorbent carbon by a two-stage process from nely divided bituminous coal, said process comprising in the rst stage, fiash-calcining the coal particles entrained in a gaseous atmosphere containing oxygen and at a temperature between about 1150 to about 2000o F. in an amount such that at least 10% of the evolved `combustible volatile matter remains unburned whereby the volatile content of the expanded particles is reduced to below about 12% by weight; in the second stage, separating the solid first-stage product from gaseous and vaporous products at a temperature not less than that at which substantially all of said vaporous products remain in the vaporous state so that the resulting carbon product will have a volatile content of less than about 12% by weight; and thereafter causing liquid oxygen to be absorbed by the resulting absorbent carbon.

7. The process according to claim 6 wherein the bituminous coal has a volatile content of between about 15 to 20% by Weight.

8. A liquid oxygen-carbon explosive comprising essentially a hard, granular, esentially non-activated carbon saturated with liquid oxygen, said carbon having a loose bulk density between about 5 to 20 lbs./ cu ft., a volatile content below about 12% by weight and an ash content below 15%, said carbon being prepared from nely divided bituminous coal capable of expanding on heating to plasticity, by means of a two-stage process comprising in the iirst stage ash-calcining the coal particles entrained in a gaseous atmosphere containing oxygen and at a temperature between about 1150 to 2000 F. in an amount sucn that at least 10% of the evolved combustible volatile matter remains unburned whereby the volatile content of the calcined expanded particles is reduced to less than 12% by weight; and in the second stage, separating the solid first-stage product from gaseous and vaporous products at a temperature not less than that at which substantially all of said vaporous products remain in the vaporous state and the resulting carbon product will have a volatile content of less than about 12% by weight.

References Cited in the tile of this patent UNITED STATES PATENTS OTHER REFERENCES C. L. Mantell: Industrial Carbon, D. Van Nostrand, Inc., N. Y. (1946), pp. 231-241. 

1. THE METHOD OF PRODUCING A LIQUID OXYGEN EXPLOSIVE WHICH COMPRISES PREPARING A HARD GRANULAR ESSENTIALLY N0N-ACTIVATED ABSORBENT CARBON BY A THREE-STAGE PROCESS FROM FINELY DIVIDED BITUMINOUS PARTICLES NORMALLY SOLID AT ORDINARY TEMPERATURES AND CAPABLE OF EXPANDING ON HEATING TO PLASTICITY, SAID PROCESS COMPRISING IN THE FIRST STAGE, FLASH-CALCINING THE PARTICLES ENTRAINED IN A GASEOUS ATMOSPHERE CONTAINING OXYGEN IN AN AMOUNT SUCH THAT AT LEAST 10% OF THE EVOLVED COMBUSTILE MATTER REMAINS UNBURNED; IN THE SECOND STAGE, SEPARATING THE SOLID FIRST-STAGE PRODUCT FROM GASEOUS AND VAPOROUS PRODUCTS AT A TEMPERATURE NOT LESS THAN THAT AT WHICH SUBSTANTIALLY ALL OF SAID VAPOROUS PRODUCTS REMAIN IN THE VAPOROUS STATE; AND IN THE THIRD STAGE, HEATING THE SOLID SECOND-STAGE PRODUCT TO REDUCE ITS VOLATILE CONTENT TO LESS THAN 5% BY WEIGHT; AND THEREAFTER CAUSING LIQUID OXYGEN TO BE ABSORBED BY THE RESULTING ABSORBENT CARBON. 